1. Field of the Invention
This invention relates to a developing device and an image forming apparatus. More particularly, this invention relates to the developing device used in the electrophotographic image forming apparatus such as a copying machine or a printer to visualize an electrostatic latent image by allowing a developer to adhere to the electrostatic latent image on a photoconductive drum surface; and the image forming apparatus using this developing device.
2. Description of the Related Art
A conventional developing device has been known to comprise a developer tank containing a developer including a toner and a carrier; a developing roller disposed in this developer tank in such a way as to be opposed to a photoconductive drum, the developing roller retaining the developer on its outer periphery and supplying the toner included in the developer in the developer tank to the photoconductive drum; and a cylindrical layer thickness-regulating member disposed to be opposed to the outer periphery of the developing roller so as to be spaced at a predetermined gap from the outer periphery and regulating a layer thickness of the developer retained on the outer periphery of the developing roller.
The developer tank in the developing device comprising this type of the cylindrical layer thickness-regulating member is generally a cast resin article, and the cylindrical layer thickness-regulating member is mounted on a part of an end wall of the developer tank. Variations in cast dimension of the developer tank, therefore, could cause variations of the predetermined gap of the cylindrical layer thickness-regulating member.
In this case, the developing device is more difficult to uniformly develop an image along an axis line of the developing roller and to stably obtain the image with a uniform concentration than a developing device comprising a plate-like layer thickness-regulating member that is relatively easy to finely adjust a gap between the layer thickness-regulating member and an outer periphery of a developing roller.
Therefore, as an example in forming the uniform layer thickness of the developer on the developing roller along the axis line, the invention disclosed in Japanese Unexamined Patent Application Publication No. Hei 7 (1995)-219341 is proposed.
Japanese Unexamined Patent Application Publication No. Hei 7 (1995)-219341 discloses a developing device provided with a layer thickness-regulating roller disposed on the upstream side of a rotating direction of a developing roller from a developing area and supported in such a way as to come in contact with the developing roller, and the layer thickness-regulating roller has grooves extending in a circumferential direction on an outer periphery of the layer thickness-regulating roller and approximately equally spaced along an axis line of the layer thickness-regulating roller.
However, even the developing device disclosed in Japanese Unexamined Patent Application Publication No. Hei 7 (1995)-219341 could not have completely avoided consequences arisen from mounting errors or deflections of the developing roller or the layer thickness-regulating roller and was difficult to obtain an image stably.